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Quickstop [UK]
Combating adversyty.
Re: One last shot... Breaking up!
This is why we need fibre optics in the car....
This is why we need fibre optics in the car....
One last shot... Breaking up!
- Thread starter BoostedSUV
- Start date
WyoSyclone
Active member
Re: One last shot... Breaking up!
Okay.... have looked over Matt's files again. I'm leaning towards the ignition feed wire to the ignition coil (also feeds the ignition module) as having an intermittent..... either in the ignition switch, the firewall connector, or inside a connector housing.....
...this could explain his starting issue (code 42 and tach jumping), could explain the apparent loss of ignition module signal to the ECM (ecm is staying powered)....
...we'll just have to wait and see..... I'm out of ideas!
Okay.... have looked over Matt's files again. I'm leaning towards the ignition feed wire to the ignition coil (also feeds the ignition module) as having an intermittent..... either in the ignition switch, the firewall connector, or inside a connector housing.....
...this could explain his starting issue (code 42 and tach jumping), could explain the apparent loss of ignition module signal to the ECM (ecm is staying powered)....
...we'll just have to wait and see..... I'm out of ideas!
BoostedSUV
Active member
Re: One last shot... Breaking up!
well I tried a few things tonight....
I put a test light on the Injector pulse wire and even during the breaking up the test light was bright and flashing. Didn't dim or stop flashing so I assume it's not loosing injector pulse.
I shook the sh*t out of the ECM wires with the truck running and I could not make the issue go away or make the idle change indicating a problem
I checked voltage to the pink wire at the coil and to the relay on the on the firewall and I had 14.2 volts, and 13.8 with the fan on. Voltage did not change when the truck was breaking up. I also checked voltage to the white wire (don't know what this would tell me?) and I had 10 volts at idle but when I brought the RPM's up it dropped down to 6.5 volts...
I also checked the mV right at the O2 harness and it was bouncing all over the place.. anywhere from 950 to 100. it just bounced around and would not steady
Another weird thing which is impossible is I was getting a 19 volt reading at the power junction block on the firewall. There's no way that can show more volts than alternator so I don't know why that happened. It was cold and wet so I came in and stopped messing with it...
well I tried a few things tonight....
I put a test light on the Injector pulse wire and even during the breaking up the test light was bright and flashing. Didn't dim or stop flashing so I assume it's not loosing injector pulse.
I shook the sh*t out of the ECM wires with the truck running and I could not make the issue go away or make the idle change indicating a problem
I checked voltage to the pink wire at the coil and to the relay on the on the firewall and I had 14.2 volts, and 13.8 with the fan on. Voltage did not change when the truck was breaking up. I also checked voltage to the white wire (don't know what this would tell me?) and I had 10 volts at idle but when I brought the RPM's up it dropped down to 6.5 volts...
I also checked the mV right at the O2 harness and it was bouncing all over the place.. anywhere from 950 to 100. it just bounced around and would not steady
Another weird thing which is impossible is I was getting a 19 volt reading at the power junction block on the firewall. There's no way that can show more volts than alternator so I don't know why that happened. It was cold and wet so I came in and stopped messing with it...
Quickstop [UK]
Combating adversyty.
Re: One last shot... Breaking up!
What could have changed? The truck idled better than ever the other night with new injectors. The miss points were higher but temp didn't affect it.
What are we missing?!
Time dependent? Truck sat for ages? Ign seems good. Any way to get an oscilloscope on the plugs? I might get one for my truck as an aid.
You're inches from this, don't give up or you'll regret it forever.
What could have changed? The truck idled better than ever the other night with new injectors. The miss points were higher but temp didn't affect it.
What are we missing?!
Time dependent? Truck sat for ages? Ign seems good. Any way to get an oscilloscope on the plugs? I might get one for my truck as an aid.
You're inches from this, don't give up or you'll regret it forever.
BoostedSUV
Active member
Re: One last shot... Breaking up!
I don't know what the hell changed from the other night... I don't think I let the truck warm up enough. Only seems to get bad when truck is warmed up..
I'm not sure I would regret giving up, it would save me from future headaches! LOL If I wasn't so determined to figure out I'd give up already.. I need to know what's doing it!
I don't know what the hell changed from the other night... I don't think I let the truck warm up enough. Only seems to get bad when truck is warmed up..
I'm not sure I would regret giving up, it would save me from future headaches! LOL If I wasn't so determined to figure out I'd give up already.. I need to know what's doing it!
BoostedSUV
Active member
Re: One last shot... Breaking up!
I messed with the RPMs again and they definitely seemed to move up in the range. its like 1300, 2100, and 2700now instead of 1100, 1500, and 2500. Very weird.. same symptons
I messed with the RPMs again and they definitely seemed to move up in the range. its like 1300, 2100, and 2700now instead of 1100, 1500, and 2500. Very weird.. same symptons
WyoSyclone
Active member
Re: One last shot... Breaking up!
Only way you can get more than 13.8 or 14 volts is if the alternator has a bad regulator, or is just going bad..... the battery can't make more than 12.1. A pilot friend of mine use to tell me "always trust your instruments"..... that 19 volt reading is telling you something.
Only way you can get more than 13.8 or 14 volts is if the alternator has a bad regulator, or is just going bad..... the battery can't make more than 12.1. A pilot friend of mine use to tell me "always trust your instruments"..... that 19 volt reading is telling you something.
WyoSyclone
Active member
Re: One last shot... Breaking up!
And... have you ever changed that O2 sensor that is giving the strange readings? How were you testing this voltage at the sensor? Between wires, or from each wire to ground?
And... have you ever changed that O2 sensor that is giving the strange readings? How were you testing this voltage at the sensor? Between wires, or from each wire to ground?
BoostedSUV
Active member
BoostedSUV
Active member
Re: One last shot... Breaking up!
I'm only showing 13.8 with elec fan on right off alternator and at the battery. It's steady voltage, but at the junction block is showing 16.9 to 19. That's impossible as the voltage can not increase itself beyond the alt output that I'm aware of??
I'm only showing 13.8 with elec fan on right off alternator and at the battery. It's steady voltage, but at the junction block is showing 16.9 to 19. That's impossible as the voltage can not increase itself beyond the alt output that I'm aware of??
WyoSyclone
Active member
Re: One last shot... Breaking up!
The mV reading at the O2 sensor confirms what your logs are showing... there is something screwed up in that circuit.... either the O2 sensor or the ECM.
The only way you can get more than specified alternator voltage is via an inductive spike, which would be indicative of a bad ground. Or, a bad coil?? I'm not sure if secondary voltage from the ignition coil could leak through to the primary and cause that, or not. I would think this type of spike would happen so fast that you almost couldn't see it on a DVM... did you ever go through and check the grounds?
The mV reading at the O2 sensor confirms what your logs are showing... there is something screwed up in that circuit.... either the O2 sensor or the ECM.
The only way you can get more than specified alternator voltage is via an inductive spike, which would be indicative of a bad ground. Or, a bad coil?? I'm not sure if secondary voltage from the ignition coil could leak through to the primary and cause that, or not. I would think this type of spike would happen so fast that you almost couldn't see it on a DVM... did you ever go through and check the grounds?
BoostedSUV
Active member
Re: One last shot... Breaking up!
I've checked just about every ground I can come up with. I even added a ground cable from the block to chasis and ran 2ga from battery to intake bolt. I also checked that the ground on the back of the head was tight. That's ECM and O2 ground. The irratic O2 mV readings are really bothering me. I will try another O2, but like I said I still have the problem with the O2 out of the picture
I've checked just about every ground I can come up with. I even added a ground cable from the block to chasis and ran 2ga from battery to intake bolt. I also checked that the ground on the back of the head was tight. That's ECM and O2 ground. The irratic O2 mV readings are really bothering me. I will try another O2, but like I said I still have the problem with the O2 out of the picture
BoostedSUV
Active member
Re: One last shot... Breaking up!
I just verified the ground is good to the O2 with the VOM and I have 4 ohms across the A nd B terminals on sensor "indicating a good sensor" according to service manual
I just verified the ground is good to the O2 with the VOM and I have 4 ohms across the A nd B terminals on sensor "indicating a good sensor" according to service manual
SloGN
9Sec Alky V6
Re: One last shot... Breaking up!
Way back when i had my 91 z28 it got to where it would do some very strange things kinda like what you are getting. it started shortly after i installed my blaster coil. so i replaced every thing like you didn't and come to find out the dang tach module in the dash was shorting out the ignition. it too would do after it had run awhile.
i dunno if the coil shorted it out or it's just a something that just happened to fail after installing the coil.
has anyone had a tach issue in these trucks?
Way back when i had my 91 z28 it got to where it would do some very strange things kinda like what you are getting. it started shortly after i installed my blaster coil. so i replaced every thing like you didn't and come to find out the dang tach module in the dash was shorting out the ignition. it too would do after it had run awhile.
i dunno if the coil shorted it out or it's just a something that just happened to fail after installing the coil.
has anyone had a tach issue in these trucks?
BoostedSUV
Active member
Re: One last shot... Breaking up!
I've been reading through service manuals for past 2 days and everything suggested in the manuals points towards what we have suggested and I have changed or tested. One thing that keeps coming it to check "ignition grounds". Where exactly would I be looking for ignition grounds? I know the ECM gets it's goung off the back of the driver side head, and I thought the ECM provided ground to the Ign module, dist, coil etc? Where else could I look? And what's the best way to test for a solid ground? I've been doing a coninuity test of the grounds but I'm not sure that's the best method for checking for a solid ground. I really think my issue is electrical at this point...
I've been reading through service manuals for past 2 days and everything suggested in the manuals points towards what we have suggested and I have changed or tested. One thing that keeps coming it to check "ignition grounds". Where exactly would I be looking for ignition grounds? I know the ECM gets it's goung off the back of the driver side head, and I thought the ECM provided ground to the Ign module, dist, coil etc? Where else could I look? And what's the best way to test for a solid ground? I've been doing a coninuity test of the grounds but I'm not sure that's the best method for checking for a solid ground. I really think my issue is electrical at this point...
BoostedSUV
Active member
Re: One last shot... Breaking up!
does the coil need to be grounded to the coil bracket? I painted my coil bracket a long time ago and I'm not sure it would provide a good ground to the coil if it does indeed use the base bolted to the bracket as a ground? I never stop thinking about this....
I've been testing grounds at the ECM and I'm thinking about running all new grounds to it just be sure... Is there a good method to testing a good ground?
does the coil need to be grounded to the coil bracket? I painted my coil bracket a long time ago and I'm not sure it would provide a good ground to the coil if it does indeed use the base bolted to the bracket as a ground? I never stop thinking about this....
I've been testing grounds at the ECM and I'm thinking about running all new grounds to it just be sure... Is there a good method to testing a good ground?
thunderace31
New member
Re: One last shot... Breaking up!
All very good questions and Im hunting poor idle stumbling issue and thinking it a ground just not sure where they all are
This will help many I think
All very good questions and Im hunting poor idle stumbling issue and thinking it a ground just not sure where they all are
This will help many I think
SY2455
70's Veteran
Re: One last shot... Breaking up!
There are 5 grounds that are on the engine. Did you check each of them ?
If you don't have the manual, they are.
1. G 100 .......... RH rear of engine, below the rocker cover. 1 Wire
2. G 101 .......... At the RH radiator support. 1 Wire
3. G107 .......... LH rear of engine, near the rocker cover. 2 Wires
4. G108 .......... Top front center of engine. 2 Wires
5. G109 .......... Top front center of engine. ^^^^^^^^ G108 and G109 are at the same point on the engine lift bracket.
There are 5 grounds that are on the engine. Did you check each of them ?
If you don't have the manual, they are.
1. G 100 .......... RH rear of engine, below the rocker cover. 1 Wire
2. G 101 .......... At the RH radiator support. 1 Wire
3. G107 .......... LH rear of engine, near the rocker cover. 2 Wires
4. G108 .......... Top front center of engine. 2 Wires
5. G109 .......... Top front center of engine. ^^^^^^^^ G108 and G109 are at the same point on the engine lift bracket.